1. Field of the Invention
This invention relates to signal transducers, and more particularly to an engine, cylinder identification (CID) transducer for providing a series of periodic signals each representative of the displacement of an engine cylinder piston through a reference piston position.
2. Description of the Prior Art
In the field of diagnostic testing of combustion engines, it is necessary to obtain information of the engine combustion cycle, to establish an engine time base reference from which the engine performance characteristics can be accurately determined. Such information is obtained in a diesel engine by measurement of the periodicity of a selected cylinder, piston stroke through a reference piston position which is obtained by monitoring a member on an engine component whose function is cyclic and directly related to the cylinder piston stroke. The periodic displacement of the engine component member monitored is detected by a proximity sensor relatively disposed in an adjacent spatial region into which the displaced member of the cyclic engine component penetrates on successive cycles. The proximity sensor, being an inductive device, provides a magnetic field in the adjacent spatial region which is altered by the periodic penetration of the component member creating an induced sensor current and a signal having a peak amplitude in dependence on the closeness, or proximity of the component member to the sensor during its displacement cycle. The proximity sensor, therefore, provides a periodic signal whose period is directly related to the periodicity of the component member displacement, and whose occurrence is directly related to the cylinder piston stroke through a reference piston position, such as top dead center (TDC).
Such sensor signals are known as cylinder identification (CID) signals. Since the CID signal amplitude is dependent on the proximity of the sensor to the member during the penetration of the member into the sensor region, the sensor is carefully mounted and tested to insure a CID signal amplitude of sufficient magnitude to provide a suitable indication. However, the spatial distance between the sensor and the member changes after installation as a result of changing levels of engine vibration caused by the changing of the engine RPM during various diagnostic tests. The changing vibration levels create relatively low frequency cyclic distortion of the sensor supporting structure which results in a similar low frequency change in the amplitude and pulse width of the CID signals. In addition, a change in engine speed itself causes a change in signal pulse width and amplitude, an increase in speed resulting in a narrowed signal pulse width due to the increase in the component member RPM.
These changes in CID signal amplitude and pulse width due to engine speed changes and vibration levels result in a non-repeatable CID detection of piston position. While the non-repeatability error may be relatively small and tolerable for many applications, the inaccuracies due to the non-repeatability are unacceptable in modern engine diagnostic systems which require accurate engine time base information to provide the required overall system accuracy for engine performance measurements and evaluation.